This invention relates to appliances such as water heaters, space heaters and fireplaces and, more particularly, to a device for controlling components commonly found in such appliances, namely, dampers and valves.
U.S. Pat. No. 6,257,871 B1 to Weiss et al, incorporated herein by reference discloses a novel and highly useful control device (sometimes referred to as a xe2x80x9cmillivoltxe2x80x9d system) for an appliance (such as a water heater or furnace), typically a gas burning appliance having a pilot light. The control device operates a damper positioned in an exhaust vent. The position of the damper can be controlled to help improve overall appliance efficiency. The appliance advantageously eliminates the need for an external power source (and attendant wiring) to control a vent damper by using thermoelectric devices such as thermopiles at the pilot light as a power source.
Motors used to move the damper in such control devices have specified operating voltages, and these millivolt systems have been found to work well near such specified operating voltages. However, the voltage to the motor is a function of the current supplied by the thermoelectric devices, and that in turn depends on the intensity of the heat applied to the thermoelectric devices (typically burning gas at a pilot light). Thus, when the pilot light is too strong voltages larger than the specified range could be delivered to the motor. The motor is supposed to shut off upon rotation of a cam to depress a switch corresponding to a predetermined condition such as an open or closed position for the damper, but high residual voltages may cause the motor to continue to operate to rotate the damper, a phenomena know as spinning.
One possible solution for the problem of spinning is adoption of voltage regulation circuitry. However, the millivolt system operates at low power levels and no commercially available components are known for use in such circuitry. Another possible approach is to modify the geometry of the cam and/or the cam/switch alignment. However, maintaining proper alignment and geometry may be difficult, especially with repeated cycling, and it may be necessary to increase operating voltage to ensure proper rotation, thereby increasing the possibility of spinning. It would be desirable to increase the acceptable operating voltage of such motors so that the control device can operate under a wider range of conditions (i.e., be less sensitive to in variations in part geometry, location and input voltage), without adding significant additional cost or complexity to the overall control device.
In accordance with a first aspect, a device for controlling a damper in an appliance comprises a motor having a rotatable shaft extending therefrom which is operatively connected to a plate of the damper, a control circuit which selectively transmits current to the motor to rotate the shaft and in turn rotate the plate to a first position and to a second position, and a dynamic brake operatively connected to the motor which acts to reduce rotation of the shaft when the current is removed from the motor.
From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology and art of damper control devices. Particularly significant in this regard is the potential the invention affords for providing a high quality, low cost, damper control device for furnaces and water heaters. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.